1. Field of the Invention
The invention relates to an apparatus for depositing a layer on a semiconductor wafer by means of vapor deposition, and to a method that uses the apparatus.
2. Description of the Related Art
US2004/0144323 A1 discloses an apparatus for depositing a layer on a semiconductor wafer, comprising an upper and a lower cover composed of transparent material and a side wall, which together define a reactor chamber. The reactor chamber is divided by a susceptor into an upper reactor chamber and a lower reactor chamber. The susceptor supports a semiconductor wafer to be coated and itself rests on arms of a supporting frame that forms the upper end of a shaft that rotates the susceptor and the semiconductor wafer. Upper and lower lamp banks heat the susceptor and the semiconductor wafer. A deposition gas is guided parallel to the surface of the semiconductor wafer through the upper reactor chamber and thermally decomposed in the process, wherein deposition products deposit to form a layer as uniformly thick as possible on the surface of the front side of the semiconductor wafer. At the same time, a purge gas is guided through the lower reactor chamber in order to prevent deposition gas or decomposition products thereof from passing to the rear side of the susceptor and to the rear side of the semiconductor wafer.
U.S. Pat. No. 4,821,674 discloses that purge gas can be guided through the shaft and through a gap existing between the shaft and a tube surrounding it, in order to prevent deposition gas from passing into the region below the susceptor.
Depositing a uniformly thick layer on a semiconductor wafer poses problems, however. Even after optimization of crucial process parameters such as the electrical power of the lamp banks and the volumetric flow rate of deposition gas and purge gas, it is ascertained after analysis of a coated semiconductor wafer that the layer thickness is somewhat greater in the center of the semiconductor wafer than in the edge region of the semiconductor wafer.